Magneto-optical recording and reproducing disk device having a bimorph type actuator with specific structures for mounting a magnetic head in opposing to the surface of the disk

Abstract

Magneto-optical disk recording and reproducing devices and actuators and distance detectors for use therewith are disclosed. The magneto-optical disk device includes a bimorph type actuator or an electromagnetic actuator for driving the magnetic head of the magneto-optical disk device. The bimorph actuator has a metallic shim having a width that varies with respect to the longitudinal distance in inverse proportion to the normal function of the first or the second free natural vibration mode. Alternatively, the bimorph type actuator has a recess formed on a bimorph element to expose a piezoelectric portion which outputs a voltage corresponding to the acceleration of the vibration of the actuator. The driver circuit of the actuator reduces the driving voltage when the frequency of the voltage generated at the recess comes into the neighborhood of a higher resonance frequency of the actuator. The optical distance detector comprises a light-emitting diode and a pair of photodiodes which detects the amount of light incident thereon after the light is reflected from a surface of an object the distance to which is measured. The geometric parameters of the photodiodes are selected such that the output of a first photodiode decreases as the measured distance increases while the output of a second photodiode increases as the measured distance increases. Thus, the normalized differential output of the two photodiodes, from which the measured distance is determined, varies substantially linearly with respect to the measured distance. In preferred forms, the photodetectors have stepped concentric configurations so that small distances can be measured accurately and efficiently.

What is claimed is: 
     
       1. A magneto-optical disk device for use with a magneto-optical disk including a layer of magnetic material defining a recording surface comprising: optical head means for radiating a recording surface of a magneto-optical disk with a light beam to heat a recording spot on the recording surface;   magnetic head means for generating, in a recording process, a biasing magnetic field at the recording spot on the recording surface of the magneto-optical disk to record information by reversing a direction of magnetization of the magnetic material on the magneto-optical disk;   distance detector means for detecting the distance between the magnetic head means and the recording surface of the magneto-optical disk;   a bimorph type actuator including a plate-shaped piezoelectric bimorph type element having a free end on which the magnetic head means is mounted to oppose the recording surface of the magneto-optical disk, the bimorph element comprising a piezoelectric portion and an electrode on the piezoelectric portion, the electrode having a recess exposing the piezoelectric portion, the piezoelectric portion generating a voltage corresponding to acceleration of the actuator; and   actuator driver means coupled to the distance detector means for driving the bimorph type actuator with a drive voltage in response to the distance detected by the distance detector means for varying the distance between the magnetic head means and the recording surface during the recording process, the actuator driver means being electrically coupled to the piezoelectric portion in the recess and reducing the drive voltage for the actuator in response to the voltage generated by the piezoelectric portion.   
     
     
       2. A bimorph type actuator for driving a recording and reproducing head of a recording and reproducing device for recording and reproducing information on and from a magneto-optical disk comprising: a plate-shaped piezoelectric bimorph element having a recess exposing a piezoelectric portion of the bimorph element, the exposed portion generating a voltage corresponding to acceleration of the bimorph element, the bimorph element having a plurality of resonance frequencies including a first resonance frequency and a higher resonance frequency;   frequency detector means, electrically coupled to the recess of the bimorph element, for detecting a frequency of the voltage generated at the exposed piezoelectric portion of the bimorph element;   distance detector means for detecting a distance between the head of the optical recording and reproducing device and the magneto-optical disk; and   actuator driver means, coupled to the distance detector means and the frequency detector means, for outputting to the piezoelectric bimorph element an actuator driving voltage corresponding to a distance detected by the distance detector means and for reducing a level of the actuator driving voltage when the frequency of the voltage generated at the exposed piezoelectric portion of the bimorph element is in a neighborhood of the higher resonance frequency of the bimorph element.   
     
     
       3. A bimorph type actuator as claimed in claim 2, further comprising a second plate-shaped piezoelectric bimorph element adjoining and extending parallel to said plate-shaped piezoelectric bimorph element having a recess formed on a surface thereof. 
     
     
       4. A magneto-optical disk device for use with a magneto-optical disk having a recording surface comprising: an optical head for radiating a recording spot of the recording surface of a magneto-optical disk with a light beam;   a magnetic head for generating a biasing magnetic field at the recording spot irradiated by the light beam on the recording surface of the magneto-optical disk;   optical distance detector means for detecting the distance between the optical distance detector means and a portion of the magneto-optical disk;   an actuator on which the magnetic head is mounted for adjusting the position of the magnetic head with respect to the disk; and   an actuator driver coupled to the optical distance detector means for driving the actuator based on the distance detected by the optical distance detector means,   the optical distance detector means comprising:   light source means for radiating light towards the disk;   first optical detector means for detecting an amount of light from the light source means incident on a light-receiving surface of the first optical detector means after reflection from the disk, the light-receiving surface being substantially perpendicular to an optical axis of the light source means;   second optical detector means for detecting an amount of light from the light source means incident on a light-receiving surface of the second optical detector means after reflection from the disk, the light-receiving surface of the second optical detector means being situated on a plane including the light-receiving surface of the first optical detector means at a position farther away from the optical axis of the light source means than the light-receiving surface of the first optical detector means;   subtractor means, coupled to outputs of the first and second optical detector means, for computing a difference between outputs of the first and second optical detector means;   adder means, coupled to outputs of the first and second optical detector means, for computing a sum of outputs of the first and second optical detector means; and   normalizer means, coupled to the subtractor means and the adder means, for computing a ratio of the difference between the outputs of the first and second optical detector means to the sum of the outputs of the first and second optical detector means wherein separations in a radial direction perpendicular to the optical axis of the light source means between the light source means and the first optical detector means and between the first and second optical detector means and areas of the first and second optical detector means are selected in such a manner that, in a measurement range of the measured distance between the disk and the optical distance detector means, the amount of light incident on the light-receiving surface of the first optical detector means decreases as the measured distance increases while the amount of light incident on the light-receiving surface of the second optical detector means increases as the measured distance increases so that the ratio, computed by the normalizer means, of the difference between the outputs of the first and second optical detector means to the sum of the outputs of the first and second optical detector means varies substantially linearly with respect to the measured distance.   
     
     
       5. A device as claimed in claim 4 wherein the outputs of said first and second optical detector means become equal to each other at a target value of said measured distance so that said ratio, computed by said normalized means, of the difference between the outputs of the first and second optical detector means to said sum of the outputs of the first and second optical detector means corresponds to a deviation of said measured distance from the target value. 
     
     
       6. A device as claimed in claim 5 wherein the light-receiving surfaces of said first and second optical detector means are stepped forward with respect to a light-emitting surface of the light source means, in the direction of the optical axis of the light source means toward the reflective surface of the disk. 
     
     
       7. A device as claimed in claim 6 wherein a height of the step between the light-receiving surfaces of the optical detector means and the light-emitting surface of the light source means in the direction of the optical axis of the light source means is greater than a thickness of the first and second optical detector means in the direction of the optical axis of the light source means. 
     
     
       8. A device as claimed in claim 4 wherein the light-receiving surfaces of said first and second optical detector means comprise surfaces disposed concentrically around the optical axis of the light source means. 
     
     
       9. A device as claimed in claim 8 wherein the light-receiving surfaces of said first and second optical detector means are stepped forward with respect to a light-emitting surface of the light source means in the direction of the optical axis of the light source means toward the reflective surface of the disk. 
     
     
       10. A device as claimed in claim 9 wherein a height of the step between the light-receiving surfaces of the optical detector means and the light-emitting surface of the light source means in the direction of the optical axis of the light source means is greater than a thickness of the first and second optical detector means in the direction of the optical axis of the light source means. 
     
     
       11. A device as claimed in claim 4 wherein the light-receiving surfaces of said first and second optical detector means are stepped forward with respect to a light-emitting surface of the light source means in the direction of the optical axis of the light source means toward the reflective surface of the disk. 
     
     
       12. A device as claimed in claim 11 wherein a height of the step between the light-receiving surfaces of the optical detector means and the light-emitting surface of the light source means in the direction of the optical axis of the light source means is greater than a thickness of the first and second optical detector means in the direction of the optical axis of the light source means. 
     
     
       13. A magneto-optical disk device for use with a magneto-optical disk including a layer of magnetic material defining a recording surface comprising: optical head means for radiating a recording spot on the recording surface of a magneto-optical disk with a light beam;   magnetic head means for generating, in a recording process, a biasing magnetic field at the recording spot on the recording surface of the magneto-optical disk to record information by reversing a direction of magnetization of the magnetic material on the magneto-optical disk;   a bimorph type actuator including a plate-shaped piezoelectric bimorph type element having a free end on which the magnetic head means is mounted to oppose the recording surface of the magneto-optical disk;   distance detector means for detecting the distance between the magnetic head means and the recording surface of the magneto-optical disk, the distance detector means comprising a support spaced from said bimorph type actuator, light emitting means mounted on the support for emitting light towards the disk and towards the bimorph type actuator, a first photosensitive element mounted on said support for receiving light from said light emitting means after reflection from said disk, and a second photosensitive element mounted on said support for receiving light from said light emitting means after reflection from a surface of said bimorph type actuator; and   actuator driver means coupled to the distance detector means for generating a drive voltage for the bimorph type actuator in response to the distance detected by the distance detector means.   
     
     
       14. A device as claimed in claim 13 wherein said light emitting means comprises first and second light emitting elements mounted on said support, and said first photosensitive element receives light from said first light emitting element reflected from said disk and said second photosensitive element receives light from said second light emitting element reflected from a surface of said bimorph type actuator. 
     
     
       15. A magneto-optical disk device for use with a magneto-optical disk including a layer of magnetic material defining a recording surface comprising: optical head means for radiating a recording surface of a magneto-optical disk with a light beam to heat a recording spot on the recording surface;   magnetic head means for generating, in a recording process, a biasing magnetic field at the recording spot on the recording surface of the magneto-optical disk to record information by reversing a direction of magnetization of the magnetic material on the magneto-optical disk;   a bimorph type actuator including a plate-shaped piezoelectric bimorph type element having a free end on which the magnetic head means is mounted to oppose the recording surface of the magneto-optical disk;   distance detector means for detecting the distance between the magnetic head means and the recording surface of the magneto-optical disk, the distance detector means comprising a light emitting element mounted on said bimorph type actuator and a photosensitive element mounted on said bimorph type actuator in a position to receive light from said light emitting element reflected from said disk; and   actuator driver means coupled to the distance detector means for driving the bimorph type actuator with a drive voltage in response to the distance detected by the distance detector means for varying the distance between the magnetic head means and the recording surface during the recording process.